Electromagnetic driving device

ABSTRACT

A constant frequency electromagnetic driving device, for example for a time piece, comprises an electromechanical transducer having a coil electromagnetically coupled to a movable mechanical element and serving both pickup and driving functions to convert mechanical movement of the movable element into an electrical signal and also to convert an electrical signal into mechanical movement of the moving element. An electric circuit shifts the phase of the electrical signal generated by movement of the moving element, amplifies the phase-shifted signal and feeds it back to the coil to drive the moving element.

United States Patent Inventors Japan Appl. No. 868,422 Filed Oct. 22, 1969 Patented Nov. 23, 1971 Priority Oct. 24, 1968 Japan ELECTROMAGNETIC DRIVING DEVICE 9 Claims, 10 Drawing Figs. US. Cl 318/128, 318/132, 331/116, 331/137, 331/142, 58/23 Int. Cl .l H02k 33/10 Field ofSearch 331/110,

Shinjl Nunokawa 8-6, Hanamigawa, Chiba;

Norlo Tabuchi, 5415, Makuharl-cho, Chiba; Tatsuo Shlmada, 2406, Todoroki, Tamagawa, Selagaya-ken, Tokyo, allot 38; 58/23 TF, 23 A0, 23 FS [56] References Cited UNITED STATES PATENTS 2,749,441 6/1956 Kelly 331/137 2,942,205 6/1960 McShan 318/128 X 2,950,447 8/1960 McGhan 331/116 3,045.19] 7/1962 Blanchard 331/137 X 3,377,535 4/1968 Yasuoka et al. 318/138 3,504,301 3/1970 Hetzel 331/116 Primary Examiner-D. F. Duggan Attorneys-Robert E. Burns and Emmanuel .l. Lobato ABSTRACT: A constant frequency electromagnetic driving device, for example for a time piece, comprises an electromechanical transducer having a coil electromagnetically coupled to a movable mechanical element and serving both pickup and driving functions to convert mechanical movement of the movable element into an electrical signal and also to convert an electrical signal into mechanical movement of the moving element. An electric circuit shifts the phase of the electrical signal generated by movement of the moving element, amplifies the phase-shifted signal and feeds it back to the coil to drive the moving element.

1 ELECTROMAGNETIC DRIVING DEVICE This invention relates to an electromagnetic driving device for a mechanical vibrator or motor. and more specifically to an electromagnetic driving device for the mechanical vibrator and rotor which are used as a reference vibrator for time pieces.

A number of driving systems have heretofore been known for driving, for example, such mechanical vibrators as tuning forks. balances, etc. as reference vibrators for clocks. One of such systems essentially comprises a transistor amplifier. a pickup or detecting coil and a driving coil connected, respectively, to the input and output sides of the amplifier, the detecting coil functioning to detect the vibratory movement of the vibrator while the driving coil drives the vibrator. This system needs two coils and is not satisfactory as a driving system for clocks which are required to be compact in design.

Another system consists of an astable multivibrator, a coil which is connected as a load to the astable multivibrator and which combines pickup and driving functions, and a vibrator fixedly secured to a magnet, the coil and magnet together constituting a transducer. The vibrator is driven when the astable multivibrator is triggered by an electric signal induced in the coil by the vibratory movement of the vibrator. In this system. which utilizes an astable multivibrator, the vibration frequency is governed by the circuit constants of the multivibrator, and the frequency of the vibrator hence varies according to variation of temperature or power source voltage or to noise. For this reason the system is not suitable for driving clocks.

This invention provides a novel and improved electromagnetic driving device which is free from the disadvantages of the conventional systems as above described.

In one aspect of the present invention, an electromagnetic driving device is provided which comprises transducing means having a moving element and at least one coil which is coupled electromagnetically with the moving element and combines pickup and driving functions whereby the coil converts a mechanical movement of the moving element into an electric signal, and also converts an electric signal applied thereto into a mechanical movement of the moving element; phase-shifting means comprising a circuit for shifting the phase of the electric signal picked up by the transducing means; and amplifying means for amplifying the electric signal shifted in phase by the phase-shifting means and then feeding it back to the transducing means; the circuit constants of the phase-shifting means being determined by the dynamic impedance of the transducing means.

By way of exemplification, it is noted that, where the moving element above referred to is a mechanical vibrator, such as a tuning fork or balance, the natural frequency of the vibrator is constant, whether at the start or during steady vibration, and the dynamic impedance which results from electromagnetic coupling of the coil and vibrator, undergoes no change. In the electromagnetic driving device of the invention, the dynamic impedance is adopted as a factor for setting the value of phase-shifting by the phase-shifting means and therefore the frequency of the vibrator remains unaffected by any variation of temperature or power source voltage or by noise. The present device thus can serve as an effective reference vibrator for a time piece.

The moving element used in the practice of the present invention may be either a mechanical vibrator equipped with a magnet, e.g., a tuning bar, tuning fork, or balance, or a rotor having magnetic poles.

The phase-shifting means may be a combination of elements stable against variations of temperature or power source voltage, e.g., a condenser-resistance, inductance coil-condenser, inductance coil-resistance, or inductance coil-condenser-resistance combination.

It is an object of the present invention to provide an electromagnetic driving device stable against variations of working conditions such as temperature. power source voltage or noise.

Another object of the invention is to provide a small-size electromagnetic driving device adapted for driving the reference driver for small time pieces.

Other features, advantages and objects of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of an electromagnetic driving device embodying the invention;

FIG. 2 is a diagrammatic side elevational view, on an enlarged scale, ofa transducer;

FIG. 3 is a graph illustrating the relationship between the vibrator frequency and dynamic impedance;

FIG. 4 is a diagrammatic plan view, on an enlarged scale, of

' a transducer equipped with a rotor;

FIG. 5 is a graph illustrating the relationship between the rotational speed of a rotor and the dynamic impedance;

FIG. 6 is a circuit diagram of another fonn ofdriving device embodying the invention;

FIG. 7 is a circuit diagram of another embodiment of driving device;

FIG. 8 is a circuit diagram of still another embodiment of driving device;

FIG. 9 is a circuit diagram of yet another embodiment of driving device; and

FIG. 10 is a circuit diagram of a further embodiment of driving device.

Referring to FIG. 1, a transducer, generally designated 1, comprises a tuning bar 4 and a coil L which is coupled electromagnetically with the tuning bar and which combines pickup and driving functions. A phase shifter 2 is shown as comprising two condensers C C, and an inductance coil L,. An amplifier 3 is shown as comprising an NPN-type transistor T and a biasing resistance R. The collector of the transistor T is connected to the emitter of the same transistor through the coil L, a DC power source shown as a battery E, and a switch S. The biasing resistance R is connected between the base and collector of the transistor. Further, the collector of the transistor is connected to the base of the same transistor through the serially connected condensers C 0,. A tap in the connection between these condensers is connected with the emitter of the transistor through the inductance coil L,.

As shown in FIG. 2, the tuning bar 4 of the transducer is fixed at one end on a base B and is equipped with a bar magnet 5 on one side of the free end and also a mass 8 for balancing with the bar magnet, on the other side. The coil L, shaped like a ring, is fixedly supported in such a position as to permit the bar magnet 5 to move freely with respect thereto in an approximately axial direction.

The dynamic impedance in the transducer will now be explained. Electric impedance of the transducer I is only the inductance of the coil L and the internal resistance thereof as long as the vibrator 4 is still. The dynamic impedance during vibration is unlike the impedance in the absence of vibration, and has the following characteristic. In the graph of FIG. 3 illustrating the relation between the frequency f of the vibrator and the dynamic impedance Zm, plotted on the axis of the abscissa and the axis of the ordinate, respectively, the dynamic impedance attains a peak at a resonance frequency f,,, representing merely a large resistance component. It is this large resistance component that has a material bearing upon the phase-shifting function of the phase shifter 2.

Therefore, in accordance with the present invention, the dynamic impedance is incorporated as one of the conditions for producing a vibration by the electromagnetic driving system. If the input voltage of the phase shifter 2 upon separation thereof from the transducer 1 is designated E,, the input voltage of the amplifier 3 is E- the output voltage of the amplifier 3 is E the output voltage of the transducer 1 is E,, the gain of the amplifier 3 is A, the transfer function of the phase shifter 2 is G,, and the transfer function of the transducer I including the dynamic impedance Zm is 0,, then we have E G E, E AE E4=G E3=AG G E and, therefore, the overall transfer function G is =,/,=A G,G,=Re 0)+j1m(c;) where Re( G) represents the real part and Im( G), the imaginary part, and j represents an imaginary unit.

Hence, the present driving system must satisfy the following conditions;

Electric power condition Re( 6); 1

Frequency condition lm(G)=0 In order to satisfy the above conditions for producing a vibration, the constants of the circuit elements of the phase shifter are determined, by way of example, on the basis of the dynamic impedance, as follows:

In a case where the vibration frequency of the driving circuit is set at l50. 8 Hz. by the dynamic impedance due to the vibration of the vibrator 4, the constants of the component elements of the driving circuit are determined as follows:

Thus, the vibration frequency is in exact agreement with the resonance frequency of the vibrator, and the phase of the electric signal of the driving circuit is shifted by 180.

The driving device operates in the following way. The resistance value of the biasing resistance R for the transistor T is set so as to permit the transistor T to conduct while the vibrator 4 is at rest. when the switch S is turned on, a current flows from the power source E into the base of the transistor T, where it is amplified, and then into the coil L. An electromagnetic force thereby produced in the coil actuates the vibrator 4. The resulting vibratory movement is converted by the coil L into an electric signal, which in turn is shifted in phase by I80 by the phase shifter 2 with the aid of the dynamic impedance of the transducer 1. The electric signal thus shifted in phase is amplified by the transistor T and fed back to the coil L so as to enable the coil to produce a sufficient electromagnetic force to drive the vibrator 4,

Another embodiment of the present invention will now be described with reference to FIG. 4, where there is shown a transducer having a rotor 16 as an alternative to the tuning bar 4 referred to above. The rotor is a ferrite disk fixedly mounted on a rotatable shaft 19 and having two pairs of positive and negative magnetic poles 17. A coil L which combines pickup and driving functions is fixed in a spaced relationship to the rotor 16. The phase shifter and amplifier to be connected to this transducer are substantially identical with those represented in FIG. 1.

The relationship between the dynamic impedance and the rotational speed of the rotor in this embodiment is plotted in FIG. with the rotational speed It on the axis of the abscissa and the dynamic impedance Zm on the axis of the ordinate. As can be seen, the dynamic impedance is proportional to the rotational speed of the rotor, and this dynamic impedance is counted, in the same way as in the preceding embodiment, as one condition for producing a rotation. Here the vibrating conditions are again as follows:

Electric power condition RAGE Frequency condition Im( )=O The constants of the circuit elements of the phase shifter are determined by the dynamic impedance at a desired speed of steady rotation of the rotor. and on the basis of those constants the phase of the electric signal in this embodiment is shifted by I80". By so doing. the present driving system satisfies the conditions for producing a vibration at a speed of steady rotation.

Originally the rotor does not have any specific rotational speed but runs with a number of revolutions which is continuously changed from the start up to steady rotation. and accordingly the dynamic impedance changes continuously. In the present driving device, on the other hand, vibration is initiated when the dynamic impedance has reached a region where both the electric power condition and the frequency condition as defined above are satisfied, whereby the rotor is enabled to sustain stable, steady rotation at a speed which is governed by the vibratory conditions above given.

Moreover, the driving device of the invention continues to work stably in spite of noise or other disturbance. As an example, a case as illustrated in FIG. 5 wherein the number of revolutions of the rotor varies with changes in the load and corresponding changes in the dynamic impedance, will now be considered. Because the phase of the present driving device is governed by the dynamic impedance and shifting by the phase shifter, a phase shifting is caused by a change in the dynamic impedance. However, the dynamic impedance incorporated in the conditions for producing a vibration as above defined serves to decrease or increase the amount of electric power required in proportion to the value of the phase shifting, so that the rotor can be controlled to an initial stable, steady rotation, As evidenced by this, there is a correlation between the phase shifting from the state of stable of rotation and the electric power condition, and the two factors in combination serve to bring the rotor back to a state of stable rotation by virtue of the dynamic impedance.

FIG. 6 shows a driving device in which the phase shifter takes the form of a T-type circuit consisting of inductance coils L I. and a condenser C The collector of a PNP-type transistor I is connected to the emitter of the transistor through a coil L a DC power source E and a switch 5, while the base of the transistor T is connected to the negative pole of the DC source E through a biasing resistance R The collector of the transistor is connected to the base through the series connected inductances L and L Further,

the collector of the transistor T is connected to a point between the inductances L and L through the capacitance 21. The coil L is electromagnetically coupled with a magnet 25 on a tuning bar 24 to constitute an electromechanical transducer.

FIG. 7 shows another form of driving system in which the phase shifter is represented by a ladder-type circuit consisting of condensers C C C and resistance R R R In the figure, numerals 34, 35, T L R E and S designate component elements substantially identical with the counterparts in FIG. 6.

In FIG. 8 there is illustrated still another form of driving device in which the phase shifter is represented by a T-type circuit consisting of inductance coils L L and a resistance R,,, and the transducer is composed of a rotor 46 having positive and negative poles as in FIG. 4 and two coils L L,,,, which are connected in series and both combine the pickup and driving functions. The coils L, and L are spaced circumferentially of the rotor a distance equal to the spacing of like poles. Other component elements indicated at T,,,, R E and S are substantially identical with the counterparts in FIG. 6.

FIG. 9 illustrates yet another form of driving device in which the phase shifter is a ladder-type circuit consisting of inductance coils L L a resistance R and a variable resistance R Other component elements 54, 55, T L R,,,,, E and S are substantially identical with the counterparts in FIG. 6. In the present device. the frequency of the vibrator 54 can be adjusted by shifting the phase through variation of the resistance value of the variable resistance R As will be understood by those skilled in the art, this form of driving device when incorporated in a clock can regulate the rate thereof.

in the embodiment of FIG. 9 the variable resistance R may be replaced by an ordinary resistance and either of the inductance coils L L can be replaced by a variable inductance coil. By the change of the inductance, the frequency of the vibrator can be adjusted as in the preceding embodiment.

FIG. 10 shows a further embodiment of driving device wherein the phase shifter takes the form of a T-type circuit consisting of an inductance coil L condensers C C and a variable resistance R In this figure, numerals 64, 65, L T R E and S signify elements substantially identical with the counterparts in FIG. 6.

In this embodiment, an ordinary condenser may be used instead of the variable resistance R and either the inductance coil or one or both of the condensers may be of variable type.

It will be understood that still other changes in the circuitry can be made, providing the conditions set out above are satisfied.

What we claim and desire to secure by letters patent is:

l. A constant frequency electromagnetic driving device comprising:

transducing means comprising a moving element and at least one coil electromagnetically coupled to said moving element and combining both pickup and driving functions, said coil convening mechanical movement of said moving element into an electrical signal and also converting an electrical signal into mechanical movement of said moving element, said transducing means having a dynamic impedance which varies with frequency;

phase shifting means for shifting the phase of the signal picked up by said transducing means, said phase shifting means having an input connected to said transducing means and comprising a combination of elements stable against variations of temperature and power source voltage;

and amplifying means for amplifying the electric signal shifted in phase by said phase shifting means and feeding the amplified signal back to said transducing means, said amplifying means having an input connected to an output of said phase shifting means and an output connected to said transducing means;'

the circuit constants of said phase shifting means being determined in accordance with the dynamic impedance of said transducing means to satisfy the conditions:

c=E, l E =A 0, G =Re( o )+jlm( Electric power condition Re( )=l Frequency condition lm( G )=0 where .4 represents the gain of the amplifying means, E, represents the input voltage of the phase shifting means, E represents the output voltage of the transducing means, G represents the transfer function of the phase shifting means, G represents the transfer function of the transducing means,

G represents the overall transfer function, j represents an imaginary unit, and Re( G) represents the real part and lm(G) represents the imaginary part of the overall transfer function G, the phase of the output signal of the amplifying means being thereby shifted at the desired frequency of said moving element by the impedance of said phase shifting means and the dynamic impedance of said transducing means, whereby the frequency of said driving device is not affected by variation of temperature or power source voltage or by noise.

2. A constant frequency electromagnetic driving device according to claim I, in which said moving element is a mechanical vibrator having a magnet coupled electromagnetically with said coil.

3. A constant frequency electromagnetic driving device according to claim 1, in which said moving element is a rotor having positive and negative poles.

4. A constant frequency electromagnetic driving device according to claim 3, in which said transducing means comprises two coils each combining both pickup and driving functions.

5. A constant frequency electromagnetic driving device according to claim 1, in which said amplifying means comprises a transistor with said coil connected in the collector-emitter circuit, and said phase shifting means comprises reactance and impedance components in the base-emitter circuit of said transistor.

6. A constant frequency electromagnetic driving device according to claim 5, in which at least one of said components of said phase shifting means is variable.

7. A constant frequency electromagnetic driving device according to claim 5, in which said phase shifting means comprises two capacitors connected in series in the ase-collector circuit of said transistor and an impedance connected from a tap between said capacitors to the emitter of said transistor.

8. A constant frequency electromagnetic driving device according to claim 5, in which said phase shifting means comprises two resistances connected in series in the base-collector circuit of said transistor and a reactance connected from a tap between said resistances to the emitter of said transistor.

9. A constant frequency electromagnetic driving device according to claim 5, in which said phase shifting means comprises two inductances connected in series in the base-collector circuit of said transistor and a resistance connected from a tap between said inductances to the emitter of said transistor.

* t i k 

1. A constant frequency electromagnetic driving device comprising: transducing means comprising a moving element and at least one coil electromagnetically coupled to said moving element and combining both pickup and driving functions, said coil converting mechanical movement of said moving element into an electrical signal and also converting an electrical signal into mechanical movement of said moving element, said transducing means having a dynamic impedance which varies with frequency; phase shifting means for shifting the phase of the signal picked up by said transducing means, said phase shifting means having an input connected to said transducing means and comprising a combination of elements Stable against variations of temperature and power source voltage; and amplifying means for amplifying the electric signal shifted in phase by said phase shifting means and feeding the amplified signal back to said transducing means, said amplifying means having an input connected to an output of said phase shifting means and an output connected to said transducing means; the circuit constants of said phase shifting means being determined in accordance with the dynamic impedance of said transducing means to satisfy the conditions: G E41E2 AG1G2 Re(G)+jIm(G) Electric power condition Re(G) 1 Frequency condition Im(G) 0 where A represents the gain of the amplifying means, E1 represents the input voltage of the phase shifting means, E4 represents the output voltage of the transducing means, G1 represents the transfer function of the phase shifting means, G2 represents the transfer function of the transducing means, G represents the overall transfer function, j represents an imaginary unit, and Re(G) represents the real part and Im(G) represents the imaginary part of the overall transfer function G, the phase of the output signal of the amplifying means being thereby shifted 180* at the desired frequency of said moving element by the impedance of said phase shifting means and the dynamic impedance of said transducing means, whereby the frequency of said driving device is not affected by variation of temperature or power source voltage or by noise.
 2. A constant frequency electromagnetic driving device according to claim 1, in which said moving element is a mechanical vibrator having a magnet coupled electromagnetically with said coil.
 3. A constant frequency electromagnetic driving device according to claim 1, in which said moving element is a rotor having positive and negative poles.
 4. A constant frequency electromagnetic driving device according to claim 3, in which said transducing means comprises two coils each combining both pickup and driving functions.
 5. A constant frequency electromagnetic driving device according to claim 1, in which said amplifying means comprises a transistor with said coil connected in the collector-emitter circuit, and said phase shifting means comprises reactance and impedance components in the base-emitter circuit of said transistor.
 6. A constant frequency electromagnetic driving device according to claim 5, in which at least one of said components of said phase shifting means is variable.
 7. A constant frequency electromagnetic driving device according to claim 5, in which said phase shifting means comprises two capacitors connected in series in the base-collector circuit of said transistor and an impedance connected from a tap between said capacitors to the emitter of said transistor.
 8. A constant frequency electromagnetic driving device according to claim 5, in which said phase shifting means comprises two resistances connected in series in the base-collector circuit of said transistor and a reactance connected from a tap between said resistances to the emitter of said transistor.
 9. A constant frequency electromagnetic driving device according to claim 5, in which said phase shifting means comprises two inductances connected in series in the base-collector circuit of said transistor and a resistance connected from a tap between said inductances to the emitter of said transistor. 